1. Field of the Invention
This invention relates to a process for recovery of amino acids from aqueous mixtures. In particular, it relates to a treatment of said amino acid containing aqueous mixture prior to extraction of the amino acid with a water immiscible organic solution containing a water insoluble extractant for said amino acid. The overall process of the invention which includes the pretreatment and extraction, also includes optional methods of recovering said extracted amino acid from the water immiscible organic solution. Accordingly, this invention also relates to a process for recovery of the amino acid by stripping of the amino acid from the organic solution.
2. Description of Related Art
Amino acids, essential to animal and human nutrition are important as food additives, feed supplements, artificial sweeteners, and intravenous solutions; thus production and purification of amino acids is an important procedure. Descriptively, amino acids are organic acids containing an amino group. These compounds can be obtained by hydrolysis of a protein, by organic synthesis, or by fermentation. As a general rule, all naturally occurring amino acids are alpha-amino acids, having the --NH.sub.2 group attached to the carbon atom next to the COOH group, beta-alanine being an exception to this generalization. Some amino acids are termed essential meaning that they are required for an organism's growth, but can not be synthesized by its body. Essential amino acids for human beings are: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
Due to present industrial procedures, it is necessary to remove amino acids from dilute fermentation broths and other aqueous mixtures. Current methods used to remove and purify amino acids are crystallization, chromatography, ion-exchange, and extraction. One such method, described in U.S. Pat. No. 2,894,954 teaches that amino acids can be removed as a solute in N-hexylamine by a plurality of liquid/liquid contacting zones. In accordance with this method the N-hexylamine is then separated from the amino acids.
Another extraction method used to separate amino acids from fermentation broths and other aqueous mixtures is discussed in: "Quantitative determinations by ion pair extraction", ACLA PHARM. SNEC. 12, 407-416 (1975), by Thomas Nordgren, and Rolf Modine which teaches the extraction of amino acids from fermentation broths by combining a water soluble extractant, tetrapentylammoniumiodide with an aqueous phase containing amino acids, and subsequently washing with methylene chloride. This method, disadvantageously has a tendency to leave water soluble ion pairs formed by the combination of extractant and amino acid in the aqueous phase, which are not extracted in the organic phase.
Another extraction method of recovering amino acids from aqueous mixtures is commonly assigned co-pending U.S. patent application Ser. No. 617,767, filed June 6, 1984, by Tuominen et al now U.S. Pat. No. 4,661,606. In this Application is disclosed a process for extraction of amino acids from aqueous solutions containing at least one amino acid with a solution of a water insoluble extractant in a water immiscible organic solution. Two phases are formed, an organic phase containing the extracted amino acid and an aqueous phase, containing the non-amino acid materials. The two phases which are immiscible are then separated and the amino acid is then recovered from the organic phase. The amino acid is recovered either by precipitation or stripping from the organic solution into a second aqueous solution from which the amino acid can be recovered by conventional purification methods.
A method of isolating L-dopa from aqueous solutions thereof employing a sulfonic acid as a liquid ion exchanger can be seen in U.S. Pat. No. 3,928,431. In this method however, sulfonic acids such as dodecylbenzene sulfonic acid, a water soluble surfactant is employed. Such material is also disclosed as a surfactant in European Patent Publication No. 73381.
Such European Patent Publication further describes several aqueous mixtures containing amino acids, which are obtained during the fermentative production of amino acids. As set forth therein, reference is made to "Chem. Abstr. 76, P 57 722k; 78, P 122655y; 78, R 146 210a; 82, P 15274j and 85, P 121 806f), L-tyrosine (see, for example, Chem. Abstr. 76, P 84 566n; 77, P 60 057y; 78, R 146 210a; 82, P 17 199 m and 85, P121 806f), 3-hydroxy-L-tyrosine=DOPA (see, for example, Chem. Abstr. 76, P 152 037z; 78, P 157 879b; 80, 144 375a; 81, P 3 699f and 83, P 7 116q), L-tryptophane (see, for example, Chem. Abstr. 78, P 56 436z, R 146 220d; 81, P 13 463m; 84, 15 655a) and 5-hydroxy-L-tryptophane (see, for example, Chem. Abstr. 76, P 139 064m; 79, P 103 669; 80, P 13 649v; 80, P 106 876g and 83, 106 65s). It is basically possible to extract the actual aqueous microorganism cultures thus obtained, but it is usually more advantageous to filter or centrifuge these before extracting and to further process the solutions obtained".